The present invention relates to novel organosilicone polymers, and their use in the manufacture of urethane cellular products, particularly flexible polyester urethane foams including flame-retarded foams.
It is well known that the urethane linkages of urethane foams are formed by the exothermic reaction of a polyfunctional isocyanate and a polyfunctional active hydrogen-containing compound in the presence of a catalyst, and that the cellular structure of the foam is provided by gas evolution and expansion during the urethane-forming reaction. In accordance with the "one-shot process" which is the most widely used industrial technique, direct reaction is effected between all of the raw materials which include the polyisocyanate, the active hydrogen-containing compound, the catalyst system, blowing agent and surfactant. A major function of the surfactant is to stabilize the urethane foam, that is, prevent collapse of the foam until the foamed product has developed sufficient gel strength to become self-supporting.
It is also well known that suitable active hydrogen-containing compounds include polyether polyols and polyester polyols. From the standpoint of their chemical structure, therefore, urethanes are usually classified as polyether and polyester urethanes, respectively. Urethane foams also differ with respect to their physical structure and, from this standpoint, are generally classified as flexible, semi-flexible or rigid foams.
Although certain techniques of urethane manufacture such as the "one-shot process" and certain components of the foam formulation such as the polyisocyanates, amine catalyst and blowing agent, are generally useful, a specific problem associated with the production of a particular type of urethane foam and the solution thereto are often peculiar to the particular chemical and physical structure of the desired foamed product. Thus, a significant development in the production of a polyether foam or a rigid foam, for example, may not be generally applicable to the production of other cellular products. In particular, the efficacy of the foam stabilizer is usually selective with respect to the formation of a particular type of foam. For example, although flexible polyester foam was originally made using conventional organic surfactants or emulsifiers, such compounds were not effective for the manufacture of flexible polyether foam. As urethane technology advanced and end-uses became more varied, it became apparent that certain deficiencies in the quality of flexible polyester foam such as the presence of splits and a non-uniform cell structure were attributable, at least in part, to the organic surfactants employed. However, the mere substitution of the organic surfactants with various polysiloxanepolyoxyalkylene block copolymers which had been used as foam stabilizers with satisfactory results in the production of other types of urethane foams (e.g., in the production of polyether urethane foams and certain rigid polyester urethane foams), did not produce completely satisfactory flexible polyester foams.
The search for improved surfactants for stabilization of polyurethane foams is further complicated by the tendency of such foams to ignite readily and burn and the need to reduce their flammability. This characteristic is particularly objectionable in the case of flexible polyurethane foams in view of the use of such foams in many applications where fire is especially hazardous such as, in regard to flexible polyester foam, their use as textile interliners. One approach to reducing flammability of flexible foams is to include a flame-retarding agent such as various phosphorus and/or halogen-containing compounds as a component of the foam-producing reaction mixture. It is found, however, that surfactants which may otherwise be effective stabilizers of non flame-retarded as well as flame-retarded foams, may not possess the further desirable property of allowing for formation of flame-retarded foam of relatively low burning extent.
For example, a significant development in polyester foam manufacture was the discovery that a satisfactory combination of uniform cell structure and freedom from splits was achieved by using a particular combination of foam stabilizing ingredients. This latter combination comprises (a) an anionic organic surfactant that is soluble in the polyester polyol reactant at room temperature and that is capable of lowering the surface tension of the polyester resin reactant when dissolved therein and (b) a polysiloxane-polyoxyalkylene block copolymer surfactant characterized by a particular molecular weight (from 600 to 17,000), siloxane content (from 14 to 40 weight percent based on the weight of the copolymer) and oxyethylene content (at least 75 weight percent based on the total amount of oxyalkylene groups in the copolymer). This particular advance in polyester foam manufacture is described in greater detail in U.S. Pat. No. 3,594,334, granted July 20, 1971. From the standpoint of potency and quality of foam product, an especially effective foam stabilizer of the class described in the latter patent is that referred to herein as comparative Surfactant AA in which silicon of the siloxane portion of the block copolymer component is substituted with methyl groups only. It is found that Surfactant AA is also capable of stabilizing flame-retarded polyester urethane foam. However, flammability properties of the foam product are deficient and appear to indicate an adverse effect of the surfactant on flame-retardant efficiency.
It is desirable, therefore, and is a primary object of this invention, to provide a new class of polysiloxane-polyoxyalkylene block copolymers which, in addition to good potency as stabilizers of flexible polyester-based urethane foam, both non flame-retarded and flame-retarded, have the further advantageous property of allowing for the formation of flame-retarded foams of relatively low burning extent.
A further object is to provide flexible polyester urethane foam of substantially reduced combustibility and a method for the manufacture of such foam.
Various other objects and advantages of this invention will become apparent to those skilled in the art from the accompanying description and disclosure.